Methods for measuring an object to be measured without making any contact can be divided into two: a passive technique such as a stereo method; and an active technique such as a triangulation method, a time-of-flight method, and a confocal method. Among them, use of the triangulation method is increasing in various fields such as product quality management and reverse-engineering.
Alight-pattern projecting method uses the principle of the triangulation method and performs a three-dimensional (3D) geometry measurement by projecting a pattern of stripes from a projector onto the object to be measured and then by capturing the pattern that changes along the geometry of the object to be measured with a camera. Japanese Unexamined Patent Application Publication No. 2009-094295 discloses a measurement apparatus for measuring a height of an electronic component based on a captured image obtained by imaging an optical cutting line when line light is projected onto the electronic component.
Because the light-pattern projecting method is capable of measuring the larger area at one time when projecting an image including a plurality of patterns of stripes on to the object to be measured, it enables a faster measurement of the 3D geometry.
In light-pattern projecting method, when a surface of the object to be measured is glossy, multiple reflections occur, that is, the projected light from the projector repeatedly reflects on a surface of the object to be measured. Due to the multiple reflections, there was a problem that measurement accuracy is reduced.
As methods to prevent the multiple reflections, a method of applying an anti-multiple-reflection spray over the surface of the object to be measured, a mask which cuts a part of the projected light from the projector in its light path, and the like have been employed. However, in the method of applying the anti-multiple-reflection spray over the surface of the object to be measured, there was a problem that the number of man-hours for rinsing increased. There was another problem that the anti-multi-reflection spray cannot be applied in an environment where a high degree of cleanness needs to be maintained.
Also, the method of using the mask is associated with a problem that the measurement time is increased since the number of times that the pattern is projected onto the object to be measured needed to be increased to cut a part of the projected light from the projector. Further, in this method, there was another problem that different masks need to be created for each individual object to be measured.